Open air optical channel

ABSTRACT

Various embodiments of apparatus and various embodiments of methods to communicate between a first circuit board and a second circuit board using one or more open air communication channels are provided. A plurality of light transmitters and light receivers are attached to a first circuit board; and a corresponding plurality of light receivers and light transmitters are attached to a second circuit board. The light receivers on both circuit boards are disposed to receive data transmitted by the corresponding light transmitters on each circuit board. In one embodiment, where the light transmitters are laser diodes, different colors may be used to increase adjacent signal rejection. In another embodiment, the light transmitters may be laser, radio, microwave, digital, ultraviolet, or infrared light transmitters. The light transmitters may transmit data across open spaces between circuit boards, including through apertures in boards placed between the light transmitter and light receiver.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a Continuation of application Ser. No. 09/822,970,filed Mar. 29, 2001, now U.S. Pat. No. 6,771,845.

FIELD OF THE INVENTION

The field of the invention relates to circuit boards generally, and moreparticularly, to apparatus and methods for communicating data over anopen space between circuit boards.

BACKGROUND OF THE INVENTION

Computers and other electrical devices operate using printed circuitboards (PCB's), thin substrates on which chips or other electroniccomponents are mounted. In the context of personal computers (PC's),some circuit boards, called backplanes, contain sockets for expansioncards, special circuit boards that, when inserted into the backplane,add new capabilities to the computer.

Backplanes are often described as active or passive. Active backplanescontain logical circuitry that performs computing functions. On theother hand, passive backplanes contain almost no computing circuitry.Most backplanes used in personal computers are active, but there hasbeen a recent move toward passive backplanes.

In a passive backplane system, active components such as the CPU areinserted on an additional card, making it easier to upgrade and torepair faulty components. Whether a backplane is active or passive, aPCB inserted into an expansion slot can communicate with another PCBinserted in the backplane via the PCB's edge connector, a tabbed edge ofthe PCB containing a plurality of parallel traces. When inserted into anexpansion slot, the traces on the edge connector connect with acorresponding plurality of traces inside the expansion slot. Theseinternal traces connect through the backplane to other expansion slotsand to other components on the backplane itself. In this manner, thebackplane's internal bus architecture can be used to communicate datafrom one PCB to another PCB located further down the backplane.

Though effective, the internal bus approach is problematic. First, thelarge number of required traces and connectors quickly consumesavailable board space. Second, though the rate of data transfer istheoretically only limited by the clock speed of the bus, bottlenecksoften cripple the rate of data transfer and impair communication betweencircuit boards. Third, inserting or removing a circuit board duringoperation of the computer or electronic device is almost unthinkable. Atthe very least, doing so may cause a minor data loss. At worst, a systemcrash may result. Consequently, it is difficult to diagnose, repair,and/or replace faulty expansion cards without first shutting down theentire system. Fourth, communication channels are only established whenthe expansion cards are properly seated within the expansion slots.Fifth, signal quality may be at risk if specific engineering guide linesare not followed such stripline or Micro-Strip. Gaps in datatransmission may occur if the card is removed or is not properly seated.

FIG. 1 illustrates a common circuit board 100, which consists of chips102, traces 103 and other components (104, 105) attached to a single ormulti-layer substrate. Traces 103 terminate at edge connector 106, whichis the part of the circuit board that is inserted into an expansion slotin a backplane. Though most expansion cards use copper traces, there hasbeen a recent move towards replacing the copper traces with a singleoptical fiber. Wave division multiplexing gives a single optical fibertremendous bandwidth, but optical fiber suffers from the same problemsaffecting copper traces. For example, PCB's using optical fiber must beproperly seated within an expansion slot to work properly, and shouldnot be inserted or removed without first shutting down the entiresystem.

Today's high availability systems operate continuously around the clock.Consequently, new developments in fault-tolerant technology arerequired. Such developments should virtually eliminate the need tophysically connect PCB's with copper traces or optical fiber, and shouldenable expansion cards to be removed or added to a system's backplanewithout disrupting system operation.

As will be evident from the figures and accompanying writtendescriptions, the open air communication channel embodied by the presentinvention supplies solutions to these and other needs long felt in theart.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and notlimitation in the figures of the accompanying drawings, in which

FIG. 1 illustrates a prior art circuit board;

FIG. 2 illustrates two circuit boards having multiple open aircommunications channels between them according to one embodiment of theinvention;

FIG. 3 illustrates two circuit boards inserted into a backplane thathave multiple open air communications channels between them according toanother embodiment of the invention;

FIG. 4 illustrates a fault tolerant backplane according to anotherembodiment of the invention;

FIG. 5 a illustrates a stack of eight circuit boards according toanother embodiment of the invention;

FIG. 5 b illustrates a sectional end view of the stack of circuit boardsshown in FIG. 5 a; and

FIG. 6 illustrates a sectional view of a stack of circuit boards havingmultiple open air communications channels between them according toanother embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Various embodiments of apparatus and various embodiments of methods tocommunicate between a first circuit board and a second circuit boardusing one or more open air communications channels are disclosed. In thefollowing detailed description, numerous specific details are set forthin order to provide a thorough understanding of the present invention.However, it will be apparent to one of ordinary skill in the art thatthese specific details need not be used to practice the presentinvention. In other circumstances, well-known structures, materials, orprocesses have not been shown or described in detail in order not tounnecessarily obscure the present invention.

Referring now to FIG. 2, two circuit boards (201, 202) are shown,according to one embodiment of the invention, having multiple open aircommunications channels (230, 240) between them. Each circuit board(201, 202) includes one or more light transmitters (210, 220) and one ormore corresponding light receivers (212, 222). In one embodiment, lightreceivers 212 and 222 are uniquely tuned to the transmitting frequenciesof corresponding light transmitters 210 and 220. As used herein, theterm “light” includes visible and invisible light. For example, a lighttransmitter may transmit data signals using visible or invisible light.

In one embodiment, Vertical Cavity Surface Emitting Lasers (VCSELs) areused as light transmitters (210, 220). Because it is desirable toimprove the signal integrity of each communication channel (230, 240) bymaximizing each channel's signal-to-noise ratio (SNR), the placement ofthe VCSELs needs to have proper spacing so that the same color VCSELdoes not interfere with an unintended neighboring light receiver of thesame frequency color. Additionally, an appropriate calumniating lenssystem may be used to attenuate the transmission beam. By picking colorsappropriately, wider columns of transmission beams can be used that willease communication and alignment with targeted light receivers. Inanother embodiment, controlled doping on VCSEL arrays may be used toease constriction of light channel matrix construction.

Using one or more communication channels between printed circuit boards(PCBs) eliminates the copper traces on the edge connectors, and achievesdata transfer rates that exceed the rates achieved by traditionalbackplane systems now in use. For example, in traditional backplanesystems, impedance in the copper traces lowers the SNR of thetransmission path, considerably slowing data transfer rates from what istheoretically possible. By sidestepping the copper backplanearchitecture altogether, embodiments of the present invention minimizeor eliminate the copper trace impedance that formerly lowered the SNR ofthe transmission path. Consequently, the SNR of the transmission path israised, and data transfer rates are increased.

Referring now to FIG. 3, two circuit boards (301, 302) are shownremovably inserted into a backplane 306, which may be attached to achassis 303 as shown. A plurality of light transmitters (310, 320, 330)and a corresponding plurality of light receivers (312, 322, 332) may becoupled with one or both sides of circuit boards (301, 302) in a varietyof combinations.

In one embodiment, one or more light transmitters may be attached toonly one side of each of circuit boards 301 and 302. In anotherembodiment, one or more light receivers may be attached to only one sideof each of circuit boards 301 and 302. In yet another embodiment, afirst side of each of circuit boards 301 and 302 may contain one or morelight transmitters, while the other side contains one or more lightreceivers. In other embodiments, one or both sides of each of circuitboards 301 and 302 may contain one or more light transmitters and lightreceivers. In any embodiment, the light receivers and light transmittersmay be placed anywhere within the X-Y plane of the circuit board towhich they are attached, including the planar surface of the circuitboard's tabbed edge connector. Additionally, one or more lighttransmitters and/or light receivers may be positioned within thethickness of an edge or edges of the circuit board substrate. Edgemounting light receivers and/or light transmitters on circuit board 301or 302 expands the number of communication channels available. Forexample, whereas a circuit board having light receivers and lighttransmitters coupled with both of its planar surfaces can communicateonly with two other adjacent boards, a circuit board having edge mountedlight receivers and light transmitters can communicate with at leastfour other circuit boards positioned around its four edges.

Light transmitters and/or light receivers may be attached to or coupledwith a circuit board using any one of a number of suitable attachment orcoupling methods well known in the art, such as, for example, bysoldering, by an adhesive, or by a physical connection, such as abracket. In one embodiment, the light receivers and/or lighttransmitters may be flush mounted within apertures in the circuit board.In another embodiment, brackets 321 may be used to attach the lighttransmitters and/or light receivers to the circuit board.

Optical fiber may be used to link light transmitters and/or lightreceivers to a circuit board where it is desirable to connect them tovarious components on the circuit board, such as other lighttransmitters and/or light receivers. For example, in FIG. 3, an opticalfiber (not shown) may be used to link light receiver 312 on one side ofcircuit board 302 with light transmitter 315 on the other side ofcircuit board 302. Where it is desirable to increase the bandwidth ofthe circuit board's internal bus architecture, the copper traces runningbetween the card's components may be supplemented or replaced withoptical fibers capable of handling 1,024 or more colors (communicationchannels).

In one embodiment, the elements needed to construct a communicationchannel include, but are not limited to: (i) a light transmitter (ii) incommunication with a corresponding light receiver (iii) over or throughan open space between the light transmitter and its corresponding lightreceiver. When constructing a communication channel, care should betaken to prevent contaminants such as dust or smoke from filteringthrough the open spaces between light transmitters and light receivers;otherwise, the integrity and reliability of the communication channelmay be compromised.

As shown in FIG. 3, a light channel 305 may be formed within backplane306 to prevent ambient light and other contaminants from disruptingcommunication channel 360. In one embodiment, light channel 305 may bean enclosed optical space bounded on at least one side by the structuralmaterial of backplane 306 (and/or expansion slot 304). In anotherembodiment, multiple communication channels may be formed within lightchannel 305.

It may be desirable to reduce or eliminate cross-over interference inembodiments where light receivers are placed adjacent each other or inclose proximity to each other. Transmission beams tend to expandradially outward over distance. In some embodiments, such expansion maycause a transmission beam to overlap light receivers adjacent or inclose proximity to the target light receiver, resulting in interferencewith signals in other communication channels. In one embodiment,cross-over interference can be reduced or substantially eliminated byassigning each light transmitter and corresponding light receiver aparticular color or broadcast frequency. For example, light transmitter310 in FIG. 3 may be a blue laser, while light transmitter 320 may be ared laser. Such an embodiment reduces cross-over interference andincreases adjacent signal rejection because light receiver 322, beingtuned to receive red laser light, will reject any blue laser light thathappens to overlap it. Other methods of increasing adjacent signalrejection include, but are not limited to: increasing the spacingbetween light receivers, attenuating the transmission beam usingappropriate lenses and/or doping methods, and placing different color(frequency) light receivers between light receivers of the same color(frequency).

Referring now to FIG. 4, a fault tolerant backplane 406 is shownaccording to another embodiment of the invention. Backplane 406 includesthree expansion slots (407, 408, 409) into which three circuit boards(401, 402, 403) are respectively removably inserted. Circuit boards 401and 403 are virtually identical in appearance, with circuit board 401having light transmitters 410, 420, 430 attached to its upper surfaceand light receivers 419, 421, 431 attached to its lower surface, andcircuit board 403 having light transmitters 417, 425, 437 attached toits upper surface and light receivers 414, 422, 434 attached to itslower surface. Circuit board 402 is positioned between boards 401 and403. Light transmitters 415 and 435 are attached to is upper surface,and light receivers 412, 432 are attached to its lower surface. Circuitboard 402 contains an aperture 405, which enables board 401 to “see”board 403.

Communication channel 440 is formed between light transmitter 410 onboard 401 and corresponding light receiver 412 on board 402.Communication channel 441 is formed between light transmitter 415 onboard 402 and light receiver 414 on board 403. Communication channel 450is formed between light transmitter 420 on board 301 and correspondinglight receiver 422 on board 403 via aperture 405 in board 402 thatallows transmission beam 450 to pass unimpeded through circuit board402. The last two communications channels 460 and 461 are formed withinthe structure of backplane 406 and may be used to power or groundcircuit boards (401, 402, 403). Channel 460 is formed between lighttransmitter 430 on board 401 and light receiver 432 on board 402.Channel 461 is formed between light transmitter 435 on board 402 andlight receiver 434 on board 403.

Backplane 406 in FIG. 4 is fault-tolerant and self-healing. For example,if board 402 is removed from backplane 406, communication between lighttransmitter 410 and light receiver 414, between light transmitter 420and light receiver 422, and between light transmitter 430 and lightreceiver 434 will be automatically reestablished at various times asboard 402 is removed. For example, channels 460 and 461 will be thefirst to merge, followed by a brief merger of channels 440 and 441 asaperture 405 passes between light transmitter 410 and light receiver414, followed by the reacquisition of channel 450, followed by a finalmerging of channels 440 and 441.

Each board can be programmed to automatically retry establishing anoperable communication channel whenever a change in signal generation isdetected. Alternatively, each board can be programmed to automaticallyreroute data traffic from an inoperable communication channel to anoperable one whenever an absence of data signal (in one embodiment,light) is detected.

Contrast the self healing aspect of the present invention with thenon-self-healing aspect of circuit boards using copper traces or opticalfiber. In these types of boards, removal of the copper trace or opticalfiber kills the channel, which remains dead as the faulty circuit boardis removed, a new one inserted, the traces or optical fiber reconnected,and the system is reinitialized.

In one embodiment, boards 401, 402, 403 may each have the same ordifferent functionalities. Similarly, expansion slots 407, 408, 409 mayeach have the same or different functionalities. For example, expansionslot 408 may have a specific signal the other expansion slots do not. Inone embodiment, a board's functionality is “slot independent”, meaningthat the functionality resides entirely within the board. In anotherembodiment, each card's functionality is determined by the expansionslot in which it is removably inserted (slot dependent functionality).In one slot dependent embodiment having eight expansion slots, two maybe used as controllers, and the remaining six divided as needed betweeninput/output and storage functions (e.g. four input/output and twostorage).

Referring now to FIGS. 5 a and 5 b, FIG. 5 a shows a perspective view ofa stack of eight circuit boards according to one aspect of theinvention. FIG. 5 b illustrates a sectional end view of the stack ofeight circuit boards shown in FIG. 5 a.

In FIG. 5 a, a stack of eight circuit boards is shown. The boards areconsecutively numbered 1–8, with board 1 on the bottom of the stack, andboard 8 on the top. One edge of each board includes one or more tabsthat may be inserted into the expansion slot(s) of a backplane. The tabsare consecutively numbered 501–508 to correspond with the appropriateboard. For example, board 1 includes tabs 501; board 2 includes tabs502, board 3 includes tabs 503, and so on.

The tabs on each board occupy one or more of five columnar positions. InFIG. 5 b, the columnar positions are represented by columns 511, 512,513, 514, and 515, which are numbered consecutively from left to right.The tabs are represented in FIG. 5 b as shaded rectangles. Eachrectangle representing a tab is shaded the same as the board to which itis attached. For example, tabs 501 in FIG. 5 a are represented in FIG. 5b as diagonally shaded rectangles because board 1 in FIG. 5 a isdiagonally shaded. Additionally, the stack of boards in FIG. 5 b isnumbered consecutively 1–8 on both sides, beginning with board 1 on thebottom and ending with board 8 on the top.

Careful arrangement of tabs 501–508 enables various pairs of boardslocated on different levels of the stack to communicate with each other.For example, tabs 501 and 505 occupy both columnar position 511 andcolumnar position 513. The absence of tabs in column 511 on boards 2, 3,and 4 allows a light transmitter (not shown) attached to the top side oftab 501 to communicate with a corresponding light transmitter (notshown) attached to the bottom side of tab 505. In this manner,communication channel 520 may be established in columnar position 511between boards 1 and 5. Similarly, board 2 may communicate directly withboard 8 using communication channel 530 in columnar position 512; board3 may communicate directly with board 6 using communication channel 550in columnar position 514; and board 4 may communicate directly withboard 7 using communication channel 560 in columnar position 515.Communication channel 540, in columnar position 513 may be used to relaya power signal from board to board.

Communication channel 540 is fault tolerant and self-healing in thatremoval of an interior board simply connects the relayed supervisorysignal to the next available board. For example, if board 3 wereremoved, the supervisory signal from board 2 would be automaticallyrelayed to board 4. In one embodiment, the supervisory signal enablesthe system to recognize the presence or absence of a board.

The other communication channels are also self-healing in that removalof an interior board will not disrupt communications. For example, board3 may be removed without disrupting communication channels 520 or 530because board 3 has no tabs in columnar positions 511 or 512. However,removal of board 3 would disrupt communication channel 550 because tab503 occupies columnar position 514 and may carry a light transmitterand/or light receiver.

Each of boards 1–8 may be equipped with notification circuitry designedto (i) detect a change in transmission intensity (e.g. such as thatcaused by the removal or fault of a light transmitter and/or lightreceiver), to (ii) automatically shutdown the affected communicationchannel, and (iii) to automatically reroute data traffic to anotheroperable channel, and/or (iv) to automatically retry to establishcommunications in the affected channel(s).

Referring now to FIG. 6, a sectional end view of a stack of eight tabbedcircuit boards is shown according to another embodiment of theinvention. The boards in the stack are consecutively numbered 1–8,beginning with board 1 on the bottom, and ending with board 8 on thetop. In this embodiment, one edge of each circuit board has one or moretabs that may be inserted within the expansion slots of a backplane (notshown). The tabs are consecutively numbered 601–608 to correspond to thecircuit board to which they are attached. For example, tab 601 isattached to board 1; tab 602 to board 2; tab 603 to board 3, and so on.

The tabbed portions of each circuit board may occupy one or more ofthree columnar positions 611, 612, 613. In FIG. 6, these tabbed portionsare represented by shaded rectangular blocks. For example, tabs 608 arerepresented by blocks filled with cross-hatched shading; tab 607 isrepresented by a block filled with uniform grey shading, and so on.

In FIG. 6, tabs 601–608 are arranged within columns 601, 602, 603 toallow communications between pairs of boards located on different levelswithin the stack. For example, light transmitters 622 on the top surfaceof tab 601 can communicate with light receivers 624 on the bottomsurface of tab 605. Similarly, light transmitters 623 on the bottomsurface of tab 605 can communicate with light receivers 621 on the topsurface of tab 601.

In this manner, a plurality of communication channels 610, 620, 630,640, may be established between tabs 601 and 605. Similar pluralities ofcommunication channels may be formed between tabs in columns 612 and613. The two communication channels 650 and 660 formed in column 613 maybe used to relay a power signal from board to board. Additionally, thecommunication channels shown in FIG. 6 are fault-tolerant andself-healing in the same way as the channels illustratively describedwith reference to FIG. 5 b.

Thus, apparatus and methods to communicate between a first circuit boardand a second circuit board using one or more open air communicationschannels are disclosed. Although the present invention is describedherein with reference to a specific preferred embodiment, manymodifications and variations therein will readily occur to those withordinary skill in the art. Accordingly, all such variations andmodifications are included within the intended scope of the presentinvention as defined by the following claims.

1. An apparatus, comprising: a first circuit board removably insertedwithin a first receptor of a backplane, the first circuit board having afirst, second, and third light receivers affixed to its bottom surface,the first light receiver to communicate using a first frequency throughair with a first light transmitter disposed on a second circuit board,the first and the second circuit boards being disposed in a backplane; asecond circuit board removably inserted within a second receptor of thebackplane, the second circuit board having a first and second lighttransmitters affixed to its top surface, the second circuit board havingan aperture therein, and having a fourth and fifth light receiversaffixed to its bottom surface, the second transmitter on the secondcircuit board to communicate using a second frequency through air withthe second light receiver disposed on the first circuit board, the firstlight receiver to reject the second frequency, the second light receiverto reject the first frequency; and a third circuit board removablyinserted within a third receptor of the backplane, the third circuitboard having a third, fourth, and fifth light transmitters affixed toits top surface, wherein a detected change in transmission intensity ofa faulted data signal automatically initiates an orderly shutdown andrerouting of the faulted data signal.
 2. The apparatus of claim 1wherein the first and/or the second light transmitter is a laser diode.3. The apparatus of claim 2 wherein the laser diode is a Vertical CavitySurface Emitting Laser (VCSEL).
 4. The apparatus of claim 1 wherein thefirst light receiver is tuned to the frequency of the first lighttransmitter.
 5. The apparatus of claim 1 wherein the first and/or thesecond light transmitter is selected from the group consisting of alaser transmitter, a radio transmitter, a digital transmitter, aninfrared transmitter, and an ultraviolet transmitter.
 6. The apparatusof claim 1 wherein the first and the second light transmitters and thefirst and the second light receivers are housed within a card or systemchassis.